bastion

Short definition from Wiktionary

Noun

1. 1
   A projecting part of a rampart or other fortification.
2. 2
   A well-fortified position; a stronghold or citadel.
3. 3
   A person, group, or thing, that strongly defends some principle.
4. 4
   Any large prominence; something that resembles a bastion in size and form.

Verb

1. 1
   To furnish with a bastion.